LESSON 3 - DSLR Camera Techniques, Part 3
(Exposure Control - The Light Meter Revealed)
Article by Stephen J. Kristof
© 2010, all rights reserved
How do you make heads or tails out of the little rectangular light meter display? Read more and you'll be using manual exposure control in no time flat!
Exploring the Digital Light Meter Display
(Exposure Control - The Light Meter Revealed)
Article by Stephen J. Kristof
© 2010, all rights reserved
How do you make heads or tails out of the little rectangular light meter display? Read more and you'll be using manual exposure control in no time flat!
Exploring the Digital Light Meter Display
Today's internal light meter is displayed as a backlit LCD indicator at the bottom of the viewfinder. In some DSLR's, the indicator is also displayed simultaneously on the back or top of the camera. It is a rectangular scale that measures from "minus 2" (-2) on one side, in single numeral increments to "zero" (0) in the middle and up to "plus 2" (+2) on the other side. See below:
Standard light meter indicator on DSLR camera
In the example above, the "meter" is indicated by the small red vertical rectangle situated in the middle immediately below the "0". This example includes ISO, shutter speed and f-stop values which, of course, change as these exposure variables are changed on the camera. Some cameras have a reverse numeration system, in which the positive and negative numbers are in opposite positions from what you see above. It makes intuitive sense to go from the lowest to the highest in a left-to-right fashion, as this is relative to all reading and numeration scales, but don't expect every manufacturer to follow this.
The red rectangle will float along the horizontal path depending on the combination of available light, ISO, shutter speed and f-stop. By the way, the rectangular indicator will likely NOT be red in your camera, but rather, black (which can be somewhat visually confusing as all of the little black rectangles look alike).
The general goal is to get the indicator as close as possible to the zero ("0"), as this indicates a proper exposure. As the indicator floats left or right along the horizontal path toward the negative 2 (-2) side, the light meter is indicating that your combination of exposure variables is insufficient for a proper exposure. Generally speaking, the further from zero toward the negative side, the darker your image will be. Conversely, the photo will appear appreciably brighter with each increment from zero toward the positive side of the meter.
IF ALL EXPOSURE VARIABLES STAY THE SAME (ie. you do not change the value of ISO, shutter speed or f-stop), if your environmental light gets brighter (ie. the sun breaks through a cloud), the light meter will move on its own toward the positive. Again, without changing the exposure variables, as the available light darkens, the light meter will move on its own toward the negative.
The light meter will also respond to changes in ISO, shutter speed and f-stop. This should be no surprise if you've been paying attention; do you remember what four factors influence exposure? If you are fuzzy on this point, review Lesson 3.1.
 available light becomes dimmer |
 available light becomes brighter |
How will the light meter respond when the ISO changes? The animated light meter below shows the direction of change corresponding to ISO changes. Pay attention to what happens when the ISO changes to a higher or lower number, in terms of the red indicator. This may seem a bit confusing at first, but it really does make sense; a HIGHER ISO setting makes the camera MORE sensitive to light, so the light meter will move toward the positive side, meaning that the image will become brighter. A LOWER ISO setting makes the camera LESS sensitive to light, so the light meter will move toward the negative side, meaning that the image will become darker.
In much the same way, your light meter will respond to changes in shutter speed. Remember our discussion regarding how LENGTH OF EXPOSURE equates to AMOUNT OF LIGHT. Thus, as you change your camera's shutter speed to higher numbers (faster speeds), the shutter will remain open for a shorter periods of time. As such, the decreased exposure to light will make the image darker. Your light meter will respond to higher shutter speeds by moving the rectangular indicator toward the negative side.
The opposite also applies! As the shutter speed is set to a lower number, more cumulative light enters the camera and the exposure gets brighter. The indicator will move toward the positive.
In these animated examples, we assume that the indicator is moving from a "proper exposure". In the reality of your photographic work, the rectangular indicator may be ANYWHERE on the light meter display, meaning that you will likely have to make changes to shutter speed or other exposure factors in order to get the indicator at or near the zero position. The basic fact remains that higher shutter speed numbers result in the indicator floating toward the negative position and lower shutter speed numbers result in the indicator floating toward the positive position.
See animation below:
How many factors influence exposure? (Remember this time?)
The answer, of course, is "four", and they are: Amount of Light, ISO, Shutter Speed and F-Stop. That means that there is one more light meter animation to look at and it relates to the f-stop.
(Need a primer on f-stops? Re-visit our camera tutorial about f-stops and apertures.) So, how does changing the f-stop impact the light meter? Just as with changes to shutter speed as illustrated above, as the aperture gets larger and smaller, the light meter will respond in kind. Because f-stops are related to the size of the hole in the lens (the aperture), changing your f-stop will make a corresponding change to the position of the light meter indicator.
As shown in the final light meter animation below, changing to a HIGHER F-STOP NUMBER (ie. from f/11 to f/22) allows LESS LIGHT into the camera. As such, the light meter indicator will slide to the negative side. Conversely, changing to a LOWER F-STOP NUMBER (ie. from f/22 to f/5.6) allows MORE LIGHT into the camera. Accordingly, the light meter indicator will slide to the positive side.
How can you get the indicator from a negative (underexposure) position to the preferred center ("0") position?
(a) Illuminate the scene using natural or artificial light (or use a flash if you must)
(b) Make the camera more sensitive to light (INCREASE the ISO number)
(c) Let light into the camera for a longer period of time (DECREASE the Shutter Speed number)
(d) Let more light into the lens by widening the aperture (DECREASE the f-stop number)
How can you get the indicator from a positive (overexposure) position to the preferred center ("0") position?
(a) Find a darker area or turn off some lights
(b) Make the camera less sensitive to light (DECREASE the ISO number)
(c) Let light into the camera for a shorter period of time (INCREASE the Shutter Speed number)
(d) Let less light into the lens by widening the aperture (INCREASE the f-stop number)
WHY BOTHER USING MANUAL EXPOSURE CONTROL WHEN AUTO-EXPOSURE IS EASIER TO USE (AND CERTAINLY EASIER TO UNDERSTAND)?
O.K., if you're new to all of this, at this point you're likely asking yourself why you should take any more time to learn about the light meter and manual exposure techniques, particularly when one considers the difficulty of understanding and accessing this more complex way of controlling light. First of all, DON'T GIVE UP! It seems harder to learn at first glance than it actually is and, with practice, actually becomes second nature. More importantly, using manual exposure allows the serious photographer to better understand and make decisions regarding how to photograph special situations and challenges in such a manner that the final result actually reflects the desired result.
Here's an example of how this can work in your favor. When you want to freeze or show motion, your priority is, of course, shutter speed. In this case, you know in advance that you need to photograph with a shutter speed of a certain value. Knowing this allows the photographer to set the shutter speed before even looking at the light meter. Thus, with the shutter speed set to a fraction that provides the desired motion effect, the photographer simply needs to adjust the f-stop and/or ISO until the light meter reading is at or near the zero point.
When you know how and why to make these exposure decisions, you become the photographer rather than the camera doing that important job for you. You are more in-control of your photography, have fewer disappointments and have a better overall chance of producing truly stunning photographs.
MY LIGHT METER IS NOT AT THE "ZERO" OR MIDDLE POSITION. WHAT SHOULD I CHANGE?
Decisions, decisions! Should I change the ISO? How about the shutter speed? Or maybe I should change the f-stop?
Well, it really depends on what you are photographing and the effect(s) you wish to achieve. Use the quick guide below to help make decisions regarding which exposure variable to adjust in order to get a proper exposure:
YOU WANT TO DO: YOUR PRIORITY SHOULD BE:
Freeze Motion FAST Shutter Speed. May also need HIGH ISO to compensate for low light
resulting from that high shutter speed. (change f-stop and watch light meter
to get proper exposure)
Show Motion LONGER Shutter Speed. May also need LOW ISO to compensate for too much
light resulting from long exposures. (change f-stop and watch light meter to
get proper exposure)
Night or Long Exposures VERY LONG Shutter Speed. May also need VERY LOW ISO to compensate for
too much light resulting from very long exposures.(change f-stop and watch
light meter to get proper exposure)
Shoot in Very Dim Light HIGH ISO (change f-stop and/or shutter speed to get a proper exposure)
Shoot in Very Bright Light LOW ISO (change f-stop and/or shutter speed to get a proper exposure)
Highest Clarity (low noise) LOW ISO (change f-stop and/or shutter speed to get a proper exposure)
Short/Long Depth of Field LOW or HIGH F-STOP (change shutter speed to get a proper exposure)
Now that you've read Parts 1-3 of this lesson,
we're wondering how well you understand Manual Exposure Control?
If you learn better by hearing the spoken word and you still feel
that you need a bit more explanation, click below to view our
10-minute video lesson on Exposure Control:
Click here to begin the next course unit - DSLR Camera Techniques, Part 4 - When to Ignore the Light Meter
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